Method of chemically polishing iron, zinc and alloys thereof



Feb. 20, 1968 R. LAcAL v 3,369,914

METHOD OF CHEMICALLY POLISHING IRON, ZINC AND ALLOYS THEREOF Filed Nov.l2, 1964 INVENTOR. RODOLPHE LACAL W /EC&'%

AGENT 3,369,914 Patented Feb. 20, 1968 3,369,914 METHUD FCHEMICALLYPOLISHING IRON, ZINC AND ALLOYS THEREOF Dodolphe Lacal,Calvados, France, assignor to North American Phiiips Company, Inc., NewYork, N.Y., a corporation of Delaware Filed Nov. 12, 1964, Ser. No.410,378 Claims priority, application France, Nov. 12, 1963, 953,317;Apr. 13, 1964 970,684

.4 Claims. (Cl. 106-3) ABSTRACT OF THE DISCLOSURE Polish iron, zinc andalloys of these metals by use of aqueous solution of hydrogen fluorideand hydrogen peroxide. This abstract is not intended to be a descriptionof the invention defined by the claims.

The surface of a metal on which a metal coating is to be deposited byreduction, exchange or electro deposition, must have a suitable surfacecondition in order that the deposition is effected under favourableconditions.

In general, the shining appearance of the metal surface is an indicationthat the surface condition is particularly suitable for providing suchdeposits. When this condition is met, the adherence of the depositedmetal is improved and the metal surface obtained by the deposition,which itself is shining, presents a great resistance against corrosion.The solderability of such thin films which are deposited on a shiningsubstrate is better than that of the films which are deposited on a dullmetal.

In addition the shining appearance of a metal surface is a criterion forthe resistance against corrosion and may be used to obtain decorativeeffects.

A method of electrolytically polishing zinc by means of acid or basicsolutions in an oxidizing medium is known as well as that for obtaininga polished surface of titanium, zirconium and alloys thereof by means ofa mixture containing hydrogen fluoride.

When treating the surface of articles which partly consist of differentalloys, the chemical polishing may be difficult if not impossible. Thevarious metals and alloys do not behave in the same manner with respectto the same acid solution. If, in addition, the various alloys arewelded to one assembly, this remains electrochemically heterogeneous andthe difference in tension at the contact places between the variouscomponents as a rule involves a preferred chemical attack.

The method of chemically polishing according to the invention isparticularly suitable for homogeneous components of iron, nickel orcobalt and also in the case that components of the same metals arecombined heterogeneously. For applying the invention to the polishing ofother alloys it is suflicient to vary the ratios of the composing partsof the polishing bath by adding, if desired, additives suitable for thepurpose in view. The invention may be applied in particular to carbonsteels and may be used for zinc.

According to the invention, the method of polishing the surface ofmetals or oxidizable metal alloys, and in particular zinc or analogousmetals, is characterized in that the surface to be polished is immersedfor a restricted period of time in an aqueous solution of hydrogenfluoride and hydrogen peroxide.

According as the metals or alloys are more or less oxidizable, thetreatment of the metal surfaces takes place in the cold or in the heat,the optimum temperature for polishing being higher for metals which areless oxidizable and being determined for each individual case. Also theconcentration of hydrogen peroxide is proportionally larger according asthe metal or the alloy to be polished is less oxidizable.

For the rest, the concentration of hydrogen fluoride may be rather weakso that the polishing operation with solution according to the inventioncan take place in a glass container or in a container which comprises aglass window through which the polishing process can be followedGenerally the ratio of molecular concentration of hy drogenperoxide-hydrogen fluoride lies between 3 and 7.

The figure in the drawing shows how the shine of the surface of an alloyvaries as a function of the ratio of the concentration of hydrogenperoxide and of hydrogen fluoride.

Preferably, the starting products of the solution are concentrated andgiven the dilution which best corresponds to the metal to be polished.These products may consist of a solution of 48 to 50% by weight ofhydrogen fluoride, i.e. containing approximately 25 g. mol. of hydrogenfluoride per litre, and a solution of hydrogen peroxide of 30%.

Preferably, for example, zinc, iron and carbon steels are treated whilecold. On the contrary, iron, nickel, cobalt are polished at atemperature of the order of 80 C. Ironnickel-cobalt alloys andiron-nickel alloys are polished at a temperature of approximately C,

When the activities are carried out in the heat, the components to bepolished are transferred to the container with the solution according tothe invention only when the temperature of the latter has been reachedand heating has been stopped.

Also the period of treatment itself must be determined for eachindividual case but it often is in the order of 1 minute.

Example First a solution of hydrogen fluoride is prepared by diluting210 ml. of the starting solution of hydrogen fluoride 48 to 50% to 1litre by deionized water. 300 ml. of this solution are added to 1 litreof the starting solution of hydrogen peroxide of 30%.

The resulting mixture is then diluted with deionized water, for examplewith 1300 ml., and heated to a temperature of approximately C. in thepolishing container which preferably consists of glass. Then heating isdiscontinued and the components to be polished, for example, componentsof iron, nickel, cobalt or an alloy of these metals, is immersed in thisbath for 1 minute.

The quality of the resulting polish depends upon the ratio of theconcentrations of hydrogen peroxide and hydrogen fluoride and it hasbeen found, that for polishing iron, nickel, cobalt and alloys ofiron-nickel a maximum shine is obtained for a molecular ratio ofhydrogen peroxide to hydrogen fluoride which is approximately 5 which isthe case noticeably with the said solution in the example.

As shown in the figure the shine Br or reflection power of the polishedsurface varies indeed as a function of the ratio of the concentrationsof hydrogen peroxide and hydrogen fluoride. In the case of the alloyiron-nickel-cobalt the maximum shine is obtained for a volume ratio V Vof the above components which equals 3 which corresponds to a molecularratio of 5. The polishing operation is preferably carried out withsolutions in which the volume ratio of hydrogen peroxide to hydrogenfluoride lies between 2 and 4 which corresponds to values 3.1 and 6.3 ofthe molecular ratio.

The action of the solution on the component to be polished is strongeron the projecting points of the surface where the catalyticdecomposition of the hydrogen peroxide is greater. This increasedoxidation also involves an increased action of the acid.

With the use of this method shining surfaces can easily be obtained evenin the case of mixed components, i.e.

component parts Which are composed of elements of different alloys.

In addition, in the composition of the solutions used within the scopeof the invention of Which the ratio of the components may vary theconcentration of hydrogen fluoride is only approximately 1% so that thisinvolves no risks in operation.

As already noted above, articles consisting of iron or iron alloys, forexample, iron-nickel-cobalt or iron-nickel, must be treated at elevatedtemperature. Polishing certain metal component parts for electronicdevices sometimes involves difficulties. Some component parts are meltedto glass component parts which, when treated with a warm mixture ofhydrogen fluoride with hydrogen peroxide, are attacked. The gas-tightand vacuum-tight properties of such a seal which are of great importancefor an electronic device, may be adversely influenced by it.

According to a further elaboration of the method according to theinvention it is possible to subject iron alloys, for example,iron-nickel and iron-nickel-cobalt, to a polishing treatment at roomtemperature, namely by a suitable pretreatment of the surface to bepolished before it is immersed in the aqueous mixture of hydrogenperoxide and hydrogen fluoride.

This pretreatment consists in that the articles are kept immersed for arestricted period of time in a mixture of chlorides and tartrates, at anelevated temperature which lies below the boiling point of the solution.

An exampleof such a pretreatment bath consists of a solution whichcontains per litre: 300 g. of tartaric acid and 6 mol of hydrochloricacid. This bath is preferably heated at a temperature of approximately60 C. The time of treatment is approximately 6 to 8 minutes.

What is claimed is:

1. A method of polishing the surface of a metal object selected from thegroup consisting of iron, zinc and oxidizable alloys thereof said methodcomprising immersing said metal object for a short period of time in anaqueous solution of hydrogen peroxide and hydrogen fluoride, themolecular ratio of hydrogen peroxide to hydrogen fluoride being betweenabout 3:1 and 7:1.

2. The method of claim 1 wherein the metal objects are oxidizable ironalloys selected from the group consistting of nickel-iron andnickel-iron-cobalt alloys.

3. The method of claim 2 wherein the metal objects are pretreated priorto the treatment with the aqueous mixture of hydrogen peroxide andhydrogen fluoride by being heated in an aqueous solution of chloridesand tartrates.

4. The method of claim 1 wherein the solution of hydrogen peroxide andhydrogen fluoride is formed by diluting with water a solution of 50% byweight of hydrogen fluoride and a solution of by weight of hydrogenperoxide.

References Cited UNITED STATES PATENTS 3,103,733 9/1963 Fauro et a1204-143 3,158,517 11/1964 Schwarzenberger 25279.3 3,228,816 1/1966Kendall 204-140.5 2,689,785 9/1954 Simon 156- 20 3,269,881 8/1966 Joneset al. 15618 XR 3,293,093 12/1966 Alderuccio et al. 15620 X OTHERREFERENCES Camp: A Study of the Etching Rate of Single-Crystal 0Germanium, in Journal of the Electro Chemical Society,

vol. 102, No. 10, 1955, pp. 586-93.

ALEXANDER H. BRODMERKEL, Primary Examiner.

J. BEVANS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,369,914 February 20 1968 Rodolphe Lacal It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

In the heading to the printed s ecifi catio "Dodolphe Lacal" should readRodo iphe Lacal niflne 4 Signed and sealed this 12th day of August 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

